The invention relates to a belt tensioner for seat belt systems in vehicles, especially an end fitting tensioner.
Belt tensioners for seat belt systems are generally known already from automotive engineering. In so-called end fitting tensioners in the case of activation of the belt tensioner the actually fixed end of a webbing usually connected to the seat frame or the vehicle body is tightened in order to provide for tensioning of the entire webbing. In the state of the art both linearly operating as well as rotatory end fitting tensioners are described. In the rotatory end fitting tensioners the webbing end is connected to a belt shaft which is driven upon activation of the belt tensioner so as to wind webbing onto the belt shaft.
For driving the belt shaft in the tensioning direction, usually a gas generator is provided for generating a gas pressure after being triggered and thus displacing a piston in a cylindrical tensioner tube along the tubular axis. The piston is connected to the belt shaft by a pull rope, for instance, so that the belt shaft is driven in the tensioning direction and belt webbing is wound onto the belt shaft.
In the state of the art, the housing for the gas generator is e.g. a cast part which has to be rather large due to its strength properties and requires comparatively expensive manufacture.
Alternatively, for example DE 10 2005 050 426 B3 as well as DE 10 2004 032 063 B4 describe rotatory belt tensioners in which a one-part bent tube is provided which simultaneously serves as tensioner tube and generator housing. The bent tube has to receive the gas generator in an accurately fitting manner, form an as tight guide as possible for the piston and the pull rope and include a gas flow passage between the generator housing and the tensioner tube. In order to achieve said different objects and functions in a satisfactory manner, narrow set tolerances have to be observed so that the manufacture of such tube is linked with considerable manufacturing efforts.